The effect of human disturbance on tree species composition and demographic structure in Kalinzu Forest Reserve,Uganda

Tree abundance and species composition in the mechanically logged, intensively pitsawn and minimally disturbed areas of Kalinzu Forest Reserve were determined. The spatial and diameter size‐class distribution of ten selected tree species representing pioneer, secondary colonizer, understorey, canopy, dominant and endangered species were also assessed. The species were: Musanga leo‐errerae, Trema orientalis, Funtumia africana, Strombosia scheffleri, Oxyansus speciosus, Parinari excelsa, Tabernaemontana holstii, Newtonia buchananii, Lovoa swynnertonii and Entandrophragma angolense. The mean stem density of all trees ≥0.5 m in height was 2809.1 per hectare and 150 species were enumerated in the three forest areas. Most individuals (47.73%) and species (75.0%) were recorded in the minimally disturbed and least in the mechanically logged areas. Of the selected species, F. africana was the most abundant (n = 789) and widely distributed in each of the areas. Entandrophragma angolense was the least abundant (n = 63) and most of its individuals (74.6%) were recorded in the minimally disturbed area. Funtumia africana and S. scheffleri (subcanopy), O. speciosus and T. holstii (understorey), N. buchananii (canopy) and P. excelsa (an upper canopy and a climax species of this forest reserve) had an inverse J‐shaped diameter size‐class structure while pioneer species (M. leo‐errerae and T. orientalis) had a bell‐shaped size‐class structure.     

Influence of shaded systems on Xylosandrus compactus infestation in Robusta coffee along a rainfall gradient in Uganda

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Tree fruiting phenology in Kalinzu Forest, Uganda

The spatial and temporal variations in species composition and abundance of trees that fruited in mechanically logged, intensively pit‐sawn and essentially undisturbed forest areas in Kalinzu Forest (0°17′S, 0°30′S and 30°00′, 30°07′E) were assessed. The duration and frequency of fruiting episodes of selected pioneer, understorey and canopy tree species were also determined. These phenology aspects were monitored for 18 months (between February 1997 and July 1998) in 99 plots, each 20 m × 20 m in size. Eighty species consisting of 1489 trees fruited during the study. Most of the species were recorded in the undisturbed forest area and least in the mechanically logged areas. Monthly number of individuals and species that fruited in each forest condition were significantly related to monthly rainfall. Two pioneer species (Musanga leo‐errerae and Trema orientalis), one sub‐canopy (Funtumia africana) and canopy (Parinari excelsa) species had extended fruiting phases (>5 months). Two understorey species (Oxyancius speciosus and Tabernaemontana spp.) had an extended phase while the third (Teclea nobilis) had a short (≤5 months) fruiting phase. Of the selected species, only Strombosia scheffleri (a sub‐canopy species) and P. excelsa had more than one fruiting episode.     

Discovery and description of giant submarine smectite cones on the seafloor in Eyjafjordur, northern Iceland, and a novel thermal microbial habitat

With the submersible JAGO and by scuba diving we discovered three remarkable geothermal cones, rising 33, 25, and 45 m from the seafloor at a depth of 65 m in Eyjafjordur, northern Iceland. The greatest geothermal activity was on the highest cone, which discharged up to 50 liters of freshwater per s at 72 degrees C and pH 10.0. The cones were built up from precipitated smectite, formed by mixing of the hot SiO2-rich geothermal fluid with the cold Mg-rich seawater. By connecting a rubber hose to one outflow, about 240 liters of pure geothermal fluids was concentrated through a 0.2-microm-pore-size filter. Among 50 thermophilic isolates, we found members of Bacillus and Thermonema and a new unidentified low-G+C gram-positive member of the Bacteria as well as one member of the Archaea, Desulfurococcus mobilis. Analysis of small-subunit rRNA genes PCR amplified and cloned directly from environmental DNA showed that 41 out of 45 Bacteria sequences belonged to members of the Aquificales, whereas all of the 10 Archaea sequences belonged to the Korarchaeota. The physiological characteristics of isolates from different parts of the cones indicate a completely freshwater habitat, supporting the possibility of subterranean transmittance of terrestrial organisms.     

Regeneration of indigenous trees in Mgahinga Gorilla National Park, Uganda

This study examines the regeneration of indigenous tree species in the formerly encroached area in Mgahinga Gorilla National Park (MGNP), south‐western Uganda. Before gazetting in 1992, MGNP had basically been agricultural land for well over 50 years. The distribution of exotic vegetation was established using a Geographical Positioning System receiver and indigenous vegetation was sampled by establishment of quadrats along transect lines. Observations indicated that approximately 2% of the old cropland was covered by exotic woodlots. Black wattle (Acacia mearnsii) and Eucalyptus trees were found to be the most widely distributed and Pinus patula the least distributed species in the park. Species numbers of indigenous trees (n = 26) were high in the old cropland, compared with twelve species observed in exotic woodlots. The natural forest supported the highest (75%) stem density and the lowest (4%) stem density was recorded in exotic woodlots. Seedling class (< 2 cm, d.b.h.) accounted for the majority of juveniles, with the lowest stem density (1350 seedlings ha^?1) recorded in exotic woodlots compared with 6609 seedlings ha^?1 in the old cropland and 24,625 seedlings ha^?1 in the natural forest. The levels of tree diversity and stocking characteristics recorded under the exotic species suggest that a low diverse community of native species may exploit this environment.